i just started 30 day singer and the first exercise they say to do is lip trills, but i can't do them, i have been practicing and i can do the lip trill for only a few seconds before i can't do them anymore, i also can't do them when trying to go up and down with my voice, is there anything else i could do instead ?

Straw singing is a great replacement for lip trills!

Here's an article on lip trills and a short lesson with extra tips as well.